Showing papers on "Phase conjugation published in 2009"
TL;DR: By constructing a temporal analog of a 4-f imaging system, wavelength-preserving spectral phase conjugation is experimentally demonstrated for compensating chromatic dispersion and self-phase modulation in optical fibers.
Abstract: We experimentally demonstrate wavelength-preserving spectral phase conjugation for compensating chromatic dispersion and self-phase modulation in optical fibers. Our implementation is based on a temporal imaging scheme that uses time lenses realized by broadband four-wave mixing in silicon waveguides. By constructing a temporal analog of a 4-f imaging system, we compensate for pulse distortions arising from second- and third-order dispersion and self-phase modulation in optical fibers.
52 citations
TL;DR: In this article, the authors demonstrate continuously tunable optical delays as large as 1.1 micros for 10 Gb/s NRZ optical signals based on four-wave mixing (FWM) process in silicon waveguide.
Abstract: We demonstrate continuously tunable optical delays as large as 1.1 micros range for 10 Gb/s NRZ optical signals based on four-wave mixing (FWM) process in silicon waveguide. The large delay range is made possible by a novel wavelength-optimized optical phase conjugation scheme, which allows for tunable dispersion compensation to minimize the residual group-velocity dispersion (GVD) for the entire tuning range.
42 citations
TL;DR: In this paper, a guide to the techniques for nonlinearity compensation in a fiber-optic communication link based on optical phase conjugation is presented. But the authors do not consider the nonlinearities compensation of amplitude-modulated and phase modulated signals.
Abstract: This article is intended as a guide to the techniques for nonlinearity compensation in a fiber-optic communication link based on optical phase conjugation. In the first part, the basics of the phase conjugation process are illustrated from both a mathematical and physical point of view. Then, the more commonly used devices for optical phase conjugation are described, with particular attention to the devices based on periodically poled lithium niobate waveguides. Subsequently, the applications of optical phase conjugation to the nonlinearity compensation of amplitude-modulated and phase-modulated signals are analyzed.
39 citations
TL;DR: Digital holography in both continuous and ns pulsed regimes at 1064 nm allows dynamic compensation of beam pointing instabilities, external perturbations introducing low order aberrations and fluctuations of the relative phase of the modes supported by the fiber.
Abstract: Amplitude and phase control of the output beam of a multimode LMA fiber supporting 4 modes is demonstrated by digital holography in both continuous and ns pulsed regimes at 1064 nm Our system allows dynamic compensation of beam pointing instabilities, external perturbations introducing low order aberrations and fluctuations of the relative phase of the modes supported by the fiber
35 citations
TL;DR: In this article, a unified formulism was introduced to describe high contrast correction methods, such as phase conjugation, classical speckle nulling and energy minimization.
Abstract: This paper introduces a unified formulism to describe many of the high contrast correction methods, namely,
phase conjugation, classical speckle nulling and energy minimization. This unified formalism led to the Electric
Field Conjugation (EFC) algorithm where the solution found is such that minimizes the sum of the estimated
electric field at a desired plane and the electric field due to the corrective elements in the system. Applying this
formalism led to the conclusion that all the other methods are special cases of EFC.
35 citations
TL;DR: It is shown that a self-pumped photorefractive phase-conjugating mirror is suitable to produce stable, high-fidelity phase conjugation of vortex beams, and it is proved that the topological charge of the vortex beam is maintained, and thus the angular momentum in the laboratory frame of reference is reversed.
Abstract: We investigate the properties of angular momentum carrying vortex beams, reflected by a phase-conjugating mirror. It is shown that a self-pumped photorefractive phase-conjugating mirror is suitable to produce stable, high-fidelity phase conjugation of vortex beams. We prove that the topological charge of the vortex beam is maintained, and thus the angular momentum in the laboratory frame of reference is reversed, as it is expected by the time reversal property of the phase-conjugating mirror. The three dimensional interference pattern in front of the phase-conjugating mirror is studied and applications in optical traps are suggested.
33 citations
TL;DR: A new phase conjugating architecture suitable for deployment as the core building block in retrodirective antenna arrays, which can be scaled to any number of elements in a modular way without impacting on complexity is verified.
Abstract: In this paper, we verify a new phase conjugating architecture suitable for deployment as the core building block in retrodirective antenna arrays, which can be scaled to any number of elements in a modular way without impacting on complexity. Our solution is based on a modified in-phase and quadrature modulator architecture, which completely resolves four major shortcomings of the conventional mixer-based approach currently used for the synthesis of phase conjugated energy derived from a sampled incoming wavefront. 1) The architecture presented removes the need for a local oscillator running at twice the RF signal frequency to be conjugated. 2) It maintains a constant transmit power even if receive power goes as low as -120 dBm. 3) All unwanted re-transmit signal products are suppressed by at least 40 dB. 4) The issue of poor RF-IF leakage prevalent in mixer-based phase-conjugation solutions is completely mitigated. The circuit has also been shown to have high conjugation accuracy (better than plusmn1deg at -60-dBm input). Near theoretically perfect experimental monostatic and bistatic results are presented for a ten-element retrodirective array constructed using the new phase conjugation architecture.
28 citations
TL;DR: Counter to intuition, it is discovered that the preferential utilization of multiply scattered light field components over their sparsely scattered counterparts via appropriate polarization selection can lead to better image reconstruction quality.
Abstract: We present experiments that study the impact of polarization selection on the phenomenon of turbidity suppression by optical phase conjugation. Counter to intuition, we discovered that the preferential utilization of multiply scattered light field components over their sparsely scattered counterparts via appropriate polarization selection can lead to better image reconstruction quality. This effect was observed with tissue phantoms and biological tissue sections. The physical origin of this effect and its dependence on scatterer properties are discussed.
27 citations
TL;DR: In this article, the interference of a speckle with the counter-propagating phase-conjugated (PC) wave produces a randomly distributed ensemble of twisted entities (ropes) surrounding optical vortex lines.
Abstract: The previously unknown property of the optical speckle pattern reported. The interference of a speckle with the counterpropagating phase-conjugated (PC) speckle wave produces a randomly distributed ensemble of a twisted entities (ropes) surrounding optical vortex lines. These entities appear in a wide range of a randomly chosen speckle parameters inside the phase-conjugating mirrors regardless to an internal physical mechanism of the wave-front reversal. These numerically generated interference patterns are relevant to the Brillouin PC mirrors and to a four-wave mixing PC mirrors based upon laser trapped ultracold atomic cloud.
25 citations
20 citations
TL;DR: In this paper, a four-wave optical parametric amplification of the ultrashort ultraviolet light pulses in bulk fused silica and CaF 2 media is achieved by means of non-collinear interaction with cylindrical beam focusing.
TL;DR: In this paper, the simultaneous combination of two nonlinear optical processes, phase conjugation and frequency conversion (Bragg scattering), produces phase sensitive gain at two new idler wavelengths in addition to the original signal wavelength.
Abstract: Phase-regenerative wavelength conversion is demonstrated experimentally. The simultaneous combination of two nonlinear optical processes, phase conjugation and frequency conversion (Bragg scattering), produces phase-sensitive gain at two new idler wavelengths in addition to the original signal wavelength. This single-stage approach does not require phase-locking of the tunable pump. At maximum pump depletion, amplitude and phase regeneration occur simultaneously.
TL;DR: In this article, the results of theoretical and experimental studies of application of parametric wave phase conjugation (WPC) for nonlinear detection of isoechogenic phantoms and for ultrasonic velocimetry of flows are reported.
Abstract: The results of theoretical and experimental studies of application of parametric wave phase conjugation (WPC) for nonlinear detection of isoechogenic phantoms and for ultrasonic velocimetry of flows are reported. Experimental WPC harmonic imaging of isoechogenic phantoms in water was demonstrated on an example of cells filled with a mixture of water and methyl alcohol. Variation of methanol concentration allows obtaining some mixtures with varied nonlinear parameters while their linear acoustic impedance remains close to the water's one. Analysis of harmonics of phase conjugate waves (PCW) in automatically con-focal WPC-system provides reliable detection of the phantoms. According to the theoretical predictions the contrasts of images are comparable with, or even stronger, than the ratio of nonlinear parameters of a phantom and its surrounding medium. 3D-simulation of propagation of PCW in heterogeneously nonlinear and moving media is developed. Break of time reversal invariance of WPC in moving media is proposed as a principle of detection and velocimetry of flows. The results of experimental linear and harmonic imaging of flows in water are presented in comparison with theoretical description.
TL;DR: It is demonstrated that single-mode broadband amplified spontaneous parametric downconversion, combined with optical parametric amplification, can be used as a classical source of phase-sensitive cross-correlated beams and measured optical coherence tomography signals with standard InGaAs photodiodes, thus realizing the first classical interferometer based on amplified parametric fluorescence.
Abstract: We demonstrate that single-mode broadband amplified spontaneous parametric downconversion, combined with optical parametric amplification, can be used as a classical source of phase-sensitive cross-correlated beams. We first study the single spatial mode emission and the spectral brightness properties of the parametric fluorescence, produced in periodically poled MgO-doped lithium niobate. Using the same single-pass bulk-crystal configuration for a pulsed optical parametric amplifier, we achieve a gain of approximately 20 dB at an average pump power of 2W, and explain the pulse narrowing observed at the output of both parametric fluorescence and amplification in the regime of high gain. Combining these two nonlinear processes, we measured optical coherence tomography signals with standard InGaAs photodiodes, thus realizing the first classical interferometer based on amplified parametric fluorescence. The results suggest their utility for demonstrating phase-conjugate optical coherence tomography.
TL;DR: Numerical simulations and experiment show that control of the outgoing beam phase using SA phase conjugation can lead to efficient compensation of turbulence effects and results in an increase of the projected laser beam power density on a remote extended target.
Abstract: Adaptive optical systems for laser beam projection onto an extended target embedded in an optically inhomogeneous medium are considered. A new adaptive optics wavefront control technique--speckle-average (SA) phase conjugation--is introduced. In this technique mitigation of speckle effects related to laser beam scattering off the rough target surface is achieved by measuring the SA wavefront slopes of the target return wave using a conventional Shack-Hartmann wavefront sensor. For statistically representative speckle averaging we consider the generation of an incoherent light source, referred to here as a Collett-Wolf beacon, directly on the target surface using a rapid steering (scanning) auxiliary laser beam. Our numerical simulations and experiment show that control of the outgoing beam phase using SA phase conjugation can lead to efficient compensation of turbulence effects and results in an increase of the projected laser beam power density on a remote extended target. The impact of both target anisoplanatism and the Collett-Wolf beacon size on adaptive system performance is studied.
TL;DR: In this article, an adaptive two-wave mixing interferometer with no field applied to a photorefractive crystal was demonstrated, in which the quadrature condition was introduced by an external π/2 phase step.
TL;DR: In this article, the authors proposed a self-phase control technique of the stimulated Brillouin scattering wave, and its principle has been demonstrated experimentally over the past several years.
Abstract: The beam combination method using stimulated Brillouin scattering phase conjugation mirrors (SBS-PCMs) is a promising technique for a commercial laser fusion driver operated with a high repetition rate around 10 Hz. The phase control of the SBS wave is essential for realization of the coherent beam combined output in the beam combination. For this reason, we proposed the 'self-phase control technique' of the stimulated Brillouin scattering wave, and its principle has been demonstrated experimentally over the past several years. In this work, the experiments are performed for the phase stabilization of wave-front dividing two-beam and four-beam combined systems by reducing the beam pointing fluctuation of the laser source using a beam expansion.
TL;DR: A robust OPC simulation technique is reported that can account for long optical path lengths by sequentially inverting the electromagnetic fields and the ideal efficiency of OPC refocusing of light through scattering medium can be accurately determined.
Abstract: The phenomenon of Optical Phase Conjugation (OPC) can be rigorously simulated using the pseudospectral time-domain (PSTD) technique. However, with finite computational memory, it is infeasible to simulate light propagating long optical paths. We report a robust OPC simulation technique that can account for long optical path lengths by sequentially inverting the electromagnetic fields. Specifically, the ideal efficiency of OPC refocusing of light through scattering medium can be accurately determined.
31 May 2009
TL;DR: A substantial improvement in the reconstruction of time-reversed THz fields is demonstrated by adapting a waveguide technique from ultrasound imaging.
Abstract: A substantial improvement in the reconstruction of time-reversed THz fields is demonstrated by adapting a waveguide technique from ultrasound imaging. Furthermore, a model based reconstruction method is considered as an alternative to time-reversal THz imaging.
TL;DR: In this article, a theoretical analysis of vectorial three-wave mixing in isotropic Kerr media is presented, which describes the amplification of a weak wave by coupling with a strong pump wave phase matched by optically induced change of average refractive index.
TL;DR: In this article, the potential of ultrasonic velocimetry and mapping for liquid flows in a model and real biological media is demonstrated experimentally and theoretically using the technique of parametric phase conjugation of sound.
Abstract: The potential of ultrasonic velocimetry and mapping for liquid flows in a model and real biological media is demonstrated experimentally and theoretically using the technique of parametric phase conjugation of sound. The basis of the proposed method is violation of invariance of an acoustic field with respect to time reversal in a moving medium that leads to an uncompensated phase shift of a phase-conjugate wave at a transmitter-receiver array. The principles for application of nonlinear acoustic effects for improving the reconstruction precision for the field of flow velocities are discussed.
TL;DR: In this article, the authors theoretically investigated the main features of pulse deceleration and pulse shape transformations during phase conjugation in photorefractive nonlinear media and showed that the effects of critical enhancement when approaching the threshold do not lead to superior light slowing down characteristics as compared to the case of two-beam coupling.
Abstract: We have theoretically investigated the main features of pulse deceleration and pulse-shape transformations during phase conjugation in photorefractive nonlinear media. The main attention in article is paid to the critical features which occur near the threshold of mirrorless oscillation. It is shown that the effects of critical enhancement when approaching the threshold do not lead to superior light slowing down characteristics as compared to the case of two-beam coupling. At the same time, essentially new features of pulse-shape transformation occur above the threshold.
02 Nov 2009
TL;DR: In this article, a volume holographic demultiplexer is proposed, in which each modal component can be separated spatially by phase matching characteristic of volume holograms combined with a phase conjugator.
Abstract: We propose a volume holographic demultiplexer in which each modal component can be separated spatially by phase matching characteristic of volume holograms combined with a phase conjugator. A dramatical improvement of the communication capacity can be expected by transmitting two or more WDM signals through one multimode fiber.
Patent•
NEC1
TL;DR: In this paper, a target detection device includes: a sound source which projects a sound pulse; a transducer array disposed in a region for receiving a forward scattered wave from an object in the propagation environment; an addition processing unit which extracts only a signal of the forward scattering wave by applying vector addition processing on a reference signal in a reference sound field received when an obstacle exists in a propagation environment.
Abstract: A target detection device includes: a sound source which projects a sound pulse; a transducer array disposed in a region for receiving a forward scattered wave from an object in the propagation environment; an addition processing unit which extracts only a signal of the forward scattered wave by applying vector addition processing on a reference signal in a reference sound field received when an obstacle exists in the propagation environment and a mixed signal in a mixed sound field received when the target exists with the obstacle; a phase conjugation determination unit which checks whether a phase conjugacy is established by receiving the signal of the extracted forward scattered wave and employing a passive phase conjugation for determining the reference sound field; and a time reversal processing unit which generates a time reversal signal on condition that the phase conjugation determination unit judges that the phase conjugacy is established.
Patent•
06 Mar 2009
TL;DR: In this article, a laser-ultrasonic wave inspection device with a phase conjugation element was proposed to record information about propagation of ultrasonic wave US in underwater conditions with high sensitivity.
Abstract: PROBLEM TO BE SOLVED: To efficiently reduce noises, while detecting a signal in underwater conditions with high sensitivity. SOLUTION: In the laser-ultrasonic wave inspection device which is equipped with a first laser light source 1 oscillating first laser beam PL for making to generate ultrasonic wave US in an inspected material 3, a second laser light source 4 oscillating second laser beam IL with which the inspected material 3 is irradiated to receive ultrasonic signal generated in the inspected material 3, an receiving optical system OP detecting information about ultrasonic wave US optically from reflected component on the surface of the inspected material 3 of the second laser beam IL, a phase conjugation element 5 converting ultrasonic signal received at the receiving optical system OP to electric signal, and a signal processing device 10 implementing signal processing output signal from the phase conjugation element 5, displaying to record information about propagation of ultrasonic wave US, the first laser light source PL is a Q switch pulse laser light source, which is a pulse width variable laser light source oscillating pulse beam with pulse width varying within a range from 100 nanoseconds to 1 microsecond. COPYRIGHT: (C)2009,JPO&INPIT
TL;DR: A polarization-controlling device was developed based on the fact that there can be a time delay between the seeder and the pumping beams during the amplification of a stimulated Brillouin scattering signal and it showed that good pumping amplification can be achieved by using this technique.
Abstract: A polarization-controlling device was developed based on the fact that there can be a time delay between the seeder and the pumping beams during the amplification of a stimulated Brillouin scattering signal. The device causes two coaxially transmitted pulsed beams with orthogonal polarizations to have the same polarization in order to implement amplification by the pumping effect. An experiment showed that good pumping amplification can be achieved by using this technique.
13 Oct 2009
TL;DR: In this paper, a unified formulism was introduced to describe many of the high contrast correction methods, namely, phase conjugation, classical speckle nulling and energy minimization.
Abstract: This paper introduces a unified formulism to describe many of the high contrast correction methods, namely, phase conjugation, classical speckle nulling and energy minimization. This unified formalism led to the Electric Field Conjugation (EFC) algorithm.
TL;DR: In this paper, the effect of phase conjugation fidelity on stimulated Brillouin scattering (SBS) threshold in a multimode optical fiber has been investigated and it is shown that SBS threshold increases at a slower rate than that predicted by equations derived for single-mode fibers with an inverse dependence on fiber length.
Abstract: We present the effect of phase conjugation fidelity on stimulated Brillouin scattering (SBS) threshold in a multimode optical fiber. As fiber lengths decrease and phase conjugation fidelity increases, SBS threshold is observed to increase at a slower rate than that predicted by equations derived for single-mode fibers with an inverse dependence on fiber length. The deviation in threshold from standard models is shown to have a direct relationship to the phase conjugation fidelity.
TL;DR: In this article, a sub-wavelength hole is drilled into a metal surface directly on top of an iron-doped lithium niobate crystal, and an interference pattern generated by the light coming from this point source and a plane reference wave is recorded.
Abstract: Holographic phase conjugation is analyzed as a method to create a photo-refractive lens with high numerical aperture. For this purpose a sub-wavelength hole is drilled into a metal surface directly on top of an iron-doped lithium niobate crystal. An interference pattern generated by the light coming from this point source and a plane reference wave is recorded. By using the phase-conjugated reference wave for read-out, a light wave being focused onto the former point source is reconstructed. In principle, a focusing system close to the theoretical diffraction limit could be implemented by this method. The performance of this arrangement is mainly determined by properties of the lithium niobate crystal, especially the crystal symmetry. Experimentally, the tight holographic focusing is demonstrated. The focus width of the reconstructed wave is shown to be below 1.2 μm, which is our spatial resolution. The diffraction efficiency obtained, however, is just 3×10−5 compared to 3×10−2 in the plane-wave case. This can be explained by experimental reasons, the inhomogeneous light intensity and limitations originating from the crystal symmetry. We estimate that the diffraction efficiency for phase conjugation through a sub-wavelength hole can be improved by three to four orders of magnitude by addressing the above-mentioned issues.